      program demo_isxdigit
      use M_strings, only : isxdigit
      implicit none
      integer                    :: i
      character(len=1),parameter :: string(*)=[(char(i),i=0,127)]
         write(*,'(40(a))')'ISXDIGIT: ',pack( string, isxdigit(string) )
      end program demo_isxdigit
